Storage controllers use a plurality of storage devices such as hard disk drives to provide a host computer with a RAID (Redundant Arrays of Inexpensive Disks)-based storage area. Storage controllers comprise a plurality of microprocessors, each of which shares data stored in shared memory. Processing time is required for the microprocessors to directly access the shared memory and use the data, and therefore a constitution in which a portion of the shared data is used by being copied to a local memory disposed close to the microprocessor has been proposed.